Can synthetic inertia stabilise grids?

November 8, 2016

With increasing reliance being placed on renewables, electricity grids are losing the conventional power plants whose rotating masses have traditionally helped smooth over glitches in grid voltage and frequency, according to a report in IEEE Spectrum. A possible solution to this problem is synthetic inertia.

Synthetic inertia is achieved by reprogramming power inverters attached to wind turbines to emulate the behaviour of synchronised spinning masses.
Montréal company Hydro-Québec TransÉnergie plans to share data on how Québec’s grid is responding to disruptive events such as powerline and power plant outages.
“We have had a couple of events quite recently and have been able to see how much the inertia from the wind power plants was working,” said Hydro-Québec professional engineer for transmission system planning Noël Aubut.

The solution is a viable one, but not enough to support massive wind power growth. Québec currently produces around 3,300MW of wind power, but Canada’s wind industry is calling for an additional 8,000MW by 2025. Turbine manufacturers are upping their synthetic inertia technology in preparation. Mr Aubut says synthetic inertia is the latest piece in a longstanding technology trend that has already transformed renewable generators from potential liabilities to power grid stability into substantial contributors to it. The first step, he told IEEE Spectrum, was equipping renewables to remain solid and thus “not harm the grid” during times of grid instability. Modern wind and solar plants are designed to “ride-through” severe faults, such as short-circuit events that drop grid voltage to zero.

With nine Australian wind farms shutting down during September’s South Australian blackout, many pundits and politicians cast blame on renewable energy. However, the Australian Energy Market Operator said the issue lay with errant wind farm control settings, which some operators have already corrected.
“In fact, most wind and solar farms can do much more than just stick around during trouble. For example, most utility-scale installations—and even some residential rooftop solar systems—are designed to combat voltage sags on power grids. Their electronic inverters can detect brownouts and generate reactive power (AC whose current wave leads its voltage wave) to raise the grid voltage,” IEEE Spectrum said in its report.

“Synthetic inertia is about responded to crashing AC frequency, usually after the loss of a big power plant. When a big generator goes offline, it leaves the grid under-supplied. That will cause the AC frequency to fall.

“Conventional power plants respond naturally and instantly to frequency dips because the momentum of their spinning turbines, synched to the grid, resist deceleration. This slows the frequency drop, buying precious seconds during which power reserves are mobilised to fill the supply gap.”
Read more from the report published in IEEE Spectrum.